When someone talks to me from the seat directly behind me nowadays, I have learnt not to answer straight away. This is after a couple of embarrassing incidents when I have answered them only to realise that they were actually talking to someone on there mobile phones and not to me. This mainly happens when they have the phone set to silent mode and they get a call or they suddenly decide they need to call someone and it cant wait a few minutes till I drop them off.
Mobile phones to me can be very anti-social things many times I have had three or four passengers in the car and instead of talking to each other they are all talking and texting to other people on their mobiles. The other anti-social thing is when passengers get in and turn there MP3 players down to tell you where they are going and then turn it right back up again for the rest of the journey.
Some have it that loud that that I can hear their music louder than the radio, that has got to be be damaging to peoples hearing.